There is a need in the medical field to measure or monitor various analytes in body fluids, such as blood or urine, for diagnostic, therapeutic or medical observation purposes. Analyte measurements may take place in the patient's body (in-vivo), out of the patient's body (ex-vivo), or in a laboratory (in-vitro), depending on the application.
In the field of diabetes management, many conventional commercial blood glucose meters require taking a blood sample and are not entirely painless. Long-term implantable glucose sensors, considered as minimally invasive methods, would allow a continuous monitoring of the human glycemia and would considerably improve the quality of life of diabetics. Continuous monitoring would allow patient's to be warned of hypo- or hyperglycemia episodes even during sleep, and it would enable real-time closed-loop insulin injection system. A continuous implantable glucose sensor would be advantageous in diabetes management and overall health of the patients when compared to the present situation where many insulin dependent diabetics still rely on 2 to 6 glucose measurements per day to manage their insulin injections.
WO 2004037079 describes an implantable glucose sensor where the viscometric measurement of a sensitive fluid, as described in Beyer et al., 2000, Biotechnol. Prog., 16, 1119-1123, is performed by means of respectively rotational (micro rheometer) and vibrational (micro cantilever) elements.
Another example of an application requiring analyte monitoring is hemofiltration, which is a renal replacement therapy used in the intensive care units. It is a slow continuous therapy in which sessions usually last between 12 to 72 hours. During hemofiltration, a patient's blood is passed through a set of tubing via a machine to a filter, where waste products and water are removed. Replacement fluid is added and the blood is returned to the patient. Hemofiltration concerns critically ill patients with sepsis, renal, cardiac and pulmonary failure, post-surgery or burns. During hemofiltration procedure, these patients are especially exposed to:                Hypo- and hypercalcemia (ideal Ca2+ concentration post-hemofilter ranges between 0.25 and 0.35 mmol/L, and ideal Ca2+ concentration in plasmatic patient ranges between 1.05 and 1.35 mmol/L);        Hypo- and hyperglycemia which may occur even in patients without diabetes mellitus (normal range 3.9 and 7.8 mmol/L);        Metabolic acidosis (normal pH range between 7.35 and 7.45).        
Calcium plays a critical role in the initiation of clotting. Citrate is used to bind calcium and prevent blood from clotting. Citrate administered pre-filter allows the filter to be regionally anticoagulated without anticoagulating the patient.
Citrate anticoagulation is an excellent alternative to heparin anticoagulation for patients at high risk of bleeding requiring continuous renal replacement therapy. However, citrate anticoagulation has some potential adverse effects such as metabolic alkalosis and acidosis, hypernatremia, hypo- and hypercalcemia. This is why during hemofiltration, ionized calcium and pH must be well controlled in order to regulate citrate delivery. In addition, renal dysfunction may cause prolonged hypoglycemia and hyperglycemia episodes which increase the risk of infection and mortality. Today, these controls are performed by hand with expensive biosensing laboratory apparatuses, usually on an hourly basis.